The present invention relates to a gasification reaction apparatus.
More particularly, the subject apparatus is for converting organic materials, or materials containing organic matter, into high calorific value gas. It is especially applicable to the disposal of wastes.
There is an ever-pressing need to dispose of wastes such as commercial and municipal (domestic) wastes. Land-fill has been a traditional means of disposal but has numerous drawbacks which are well known. Incineration is a possibly better method of disposal, but has its limitations. In particular, energy conversion rates are comparatively low, and the utilization of waste heat, such as for district heating, is beset with efficiency problems and high capital costs of heat distribution. Incinerators produce large volumes of flue gases of low calorific value. They must be cleaned, expensively, before discharge to the atmosphere. Incinerators also yield large quantities of ash, which require disposal.
Incineration therefore is by no means an ideal alternative to land-fill.
Gasification is a potentially attractive alternative to incineration. In gasification, organic matter is decomposed directly, i.e. converted pyrolytically in the absence of air, into combustible gas and ash. Unfortunately, with present gasifiers the gas produced is heavily contaminated with carbon and ash particles. The gas needs considerable and costly cleaning before it can be efficiently utilized as a source of heat or for conversion into electricity. Frequently, the gas produced by existing gasification plant is contaminated with highly toxic dioxins.
The present invention has for its object the development of a highly efficient converter or gasifier capable of yielding clean, high calorific value gas with minimal ash. Another object is to devise an adaptable converter or gasifier design suitable for implementation in large-scale municipal waste disposal sites, as well as for implementation in small sites such as in hotels, factories and shopping precincts. In the latter implementation, the gasifier desirably would provide all the energy needs of the site, and could make it substantially self-sufficient.
A municipal waste disposal plant embodying the present gasification reaction apparatus can be organised as described in the following overview.
Incoming solid waste is passed to a sorting station. Here, ferrous and non-ferrous metal objects are removed. Also removed are ceramic and vitreous objects. The remaining solid waste is primarily of organic matter, including cellulosic, plastics and rubber materials. The waste is now passed to a shredding station, to be broken down into small particles of relatively uniform size. At this stage, the waste will normally contain large amounts of moisture, so it is passed to a drier. Energy for the drier is taken from the exhaust of the boiler/engine and used for the further conversion of gas to usable energy, ie electricity or heat. Moisture driven off as water vapour may be condensed for discharge to a sewer.
The dried waste, if in the form of a cake is comminuted, and is then delivered to the gasifier for decomposition into flammable gas and ash. The gas which is produced can be used for various purposes, but the primary use is for driving a gas turbine generator for producing electricity, some or all of which may be supplied for gain to the national grid system. Some of the gas is used for heating the gasification apparatus. Exhaust from the later can be used to heat the drier indirectly. Exhaust from the gas turbine generator can be fed to a heat exchanger for producing superheated steam, for powering a steam turbine generator. Some of the steam might be used for heating the drier. Electricity produced by the steam turbine generator may be utilised for the plant installation""s needs or may be supplied for gain to the grid system.
It will be seen from the foregoing outline that a gasification plant is economically highly desirable. Acquisition of the fuel, (waste), may cost the plant operator nothing. Indeed, the operator may well be able to charge waste producers for disposing of the waste. Once up and running, the plant need have no significant operational costs other than staffing and routine maintenance and repair. The energy input for operating the plant can be derived effectively from the waste itself. Surplus energy derived from the waste can be sold for profit, e.g. as electrical or thermal energy.
By this invention, a method of gasifying solid or liquid organic matter for producing high calorific value product gas, involves the steps of heating a gasification vessel to elevated temperature while excluding air therefrom, admitting feedstock airlessly to the top of the vessel and centrifugally dispersing the feedstock by a fan into immediate contact with the heated inside of the vessel, for decomposition into gas and ash, and exerting a cyclone motion on the product gas within the vessel for cracking it and for ridding it substantially of particulate matter such as ash, the gas being conducted to an outlet along a central axial path through the vessel.
The present invention provides at an improved gasification reaction apparatus. According to the invention, therefore, there is provided a gasification reactor apparatus, comprising a combustion chamber wherein is mounted a gasification vessel which has an inlet for feedstock to be gasified and an outlet for discharging product gas, the inlet including air-isolating and sealing means for preventing ingress of air to the vessel with feedstock, and in an upper part of the vessel there is a combination rotary fan and cyclone unit which, in use, respectively (a) disperses incoming feedstock into contact with a heated inside wall of the vessel and (b) establishes a cyclone in the product gas for ridding the gas of particulate matter before discharge from the outlet.